F4IOZOlivier · radio amateur · JN18FS

The footprint who sees the satellite?

A real satellite is over a point of the Earth: paint the area that sees it, then discover its true footprint. The higher it is, the larger it is! All games

Where can the satellite be heard?

Draw the area's outline (or paint it), then “Reveal”. The more your area overlaps the true footprint, the more you score: PERFECT beyond 85%!

Badges

First footprintA first footprint painted.
Right in the circleAn overlap of 85% or more.
Combo ×4Reach the ×4 multiplier.
Under the ISSGREAT or better on the ISS's footprint.
A third of the EarthGREAT or better on QO-100's footprint.
Above the roofsFour GREAT rounds or better in an above-10° game.
Who can talk?Eight right answers out of eight in « Who can talk? ».
Cartographer5,000 points in a game.
Sky regularTen games.
All-rounderFinish a game of each game.

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A satellite's footprint

A satellite can be heard wherever it is above the horizon. Seen from space, that is a cap round the point beneath it: its radius, seen from the Earth's centre, is λ = acos(R/(R+h)) (R = 6,378 km, h the height).

Above 10° only (the trees, the roofs, the noise of the horizon): λ = acos(R·cos ε/(R+h)) − ε, with ε = 10°. The footprint shrinks a lot in low orbit.
Two stations can talk through the satellite as long as both are in its footprint at the same time: the mutual footprint.
The mark: the overlap of your area and the true one, intersection over union (IoU), counted on the sphere. PERFECT beyond 85%, GREAT 70%, GOOD 55%, OK 35%.

Height	Radius at 0°	Radius at 10°	Share of the Earth
ISS 420 km	2,254 km (20.2°)	1,390 km	3.1 %
SO-50 600 km	2,664 km (23.9°)	1,762 km	4.3 %
AO-07 1,450 km	3,945 km (35.4°)	2,966 km	9.3 %
QO-100 35,786 km	9,050 km (81.3°)	7,952 km	42.4 %

The real thing The low-orbit satellites are worked out in your browser (SGP4, satellite.js) with the site's orbital elements, at an instant of the next 24 hours; QO-100 is geostationary, over 0° N, 25.9° E, at 35,786 km.